A combination picture of mosaics depicting St. Celestine V and Pope Benedict XVI.

ROME (CNS) — The halls of history might hold some clues as to what kind of impact Pope Benedict XVI's resignation will have on the church and how to navigate a smooth transition, said a U.S. scholar.

"All these problems surrounding how to treat Benedict, what to call him, how he will be dealt with in his life after the papacy, how his death will be dealt with, all of these are new" questions, said Joshua Birk, a fellow at the American Academy in Rome and expert in medieval Mediterranean history.

To find some answers or at least some guidance, "we sort of have to go back to these medieval cases (of papal resignation) because we literally have nothing else" to go by, he told Catholic News Service Feb. 15.

There's not much in the annals to sift through, however. Papal resignations are extremely rare with only four in the past 1,100 years, he said. And almost every case involved popes who were pressured to step down.

Only the voluntary resignation of St. Celestine V in 1294, he said, can offer relevant parallels to help the church make sense of the free and willful resignation of Pope Benedict.

The case of Pope Celestine also resulted in some innovative changes that he brought with his decision to resign, he said.

For example, Birk said, the principles behind Pope Celestine's decision to step down and "how Celestine articulated the ability of a pope to resign are incredibly important," as is the papal bull he issued establishing rules for an abdication.

The late 13th-century pope also "established the ground rules for how papal conclaves will operate in selecting the pope," said Birk, who teaches history at Smith College in Northampton, Mass.

The formal process used for centuries to select a new pope, a process that generally follows the death of a pope, is actually the model St. Celestine established for "how to select a pope after a resignation," he said.

Before Pope Celestine, the selection process was "less formalized" and often operated much differently from one papal selection to the next, he said.

"Celestine is the one who really lays down the papal bulls establishing the rights of the conclave and how they'll act under these circumstances" of a vacant see, he said.

Just as Pope Celestine's bold move carried with it important and lasting norms and traditions, so too, may Pope Benedict's decision usher in a new approach, the scholar said.

"For a pope that is generally viewed as incredibly conservative and very traditionalist, this resignation actually shows a remarkable innovation on his part," Birk said.

While the idea of resignation may have been bandied about with other popes, only Pope Benedict has really embraced it with the "modern understandings of health, illness and the abilities of modern science to prolong life even in times of sickness," he said.

"The innovation Benedict has shown in resigning may give the College of Cardinals more leeway and may allow them to be more innovative and perhaps more forward-thinking in their selections," he said.

It's difficult to evaluate the problems caused directly by Pope Celestine's resignation and those caused by his successor, Pope Boniface VIII, the historian said. Boniface imprisoned his predecessor out of fear his many political enemies might "use Celestine against him," try to set him up "as an antipope or even make the argument that Celestine's resignation is illegitimate and that Boniface isn't exactly pope."

The church will have to grapple with what having a retired pope in the wings will mean, he said.

Though there is no danger of any harsh medieval treatment, the church will have to simply look at "how this transfer is negotiated" or handled and Celestine's case "can be tremendously useful for us to look at."

Birk said Pope Benedict felt a great affection for St. Celestine.

He declared a Celestine Year from August 2009 to August 2010 to commemorate the 800th anniversary of the saint's birth and he visited the saint's relics twice during his pontificate. During a trip to L'Aquila in 2009, Pope Benedict placed the long woolen pallium he received when he was elected on the saintly pope's casket and left it there as a gift.

Pope Celestine is mostly remembered for "his reluctance to take up this sort of burden of the Apostolic See" and "actually flees when he hears word he is going to be made pope," Birk said.

He was plucked at the age of 79 from his secluded life as a Benedictine monk and hermit and thrust into the pontificate after the College of Cardinals broke a two-year-long deadlock and elected him in 1294.

While he never fled, Pope Benedict never kept his reluctance to become pope a secret.

The then-78-year-old pontiff told a group of German pilgrims the day after his installation that he equated the growing consensus among cardinals to elect him pope as "an axe" getting ready to fall on his head. He had been looking forward to a life of peaceful retirement and said he felt "inadequate" for a job that demanded great "dynamism" and strength.

Pope Benedict's coat of arms features a bear carrying a pack, symbolizing the weight of the episcopate. Pope Benedict has said the image gave him the encouragement to carry out his ministry like a beast of burden, but with confidence and joy.